The dominant material used commercially for comfort cushioning, such as furniture cushions, automotive cushions, mattresses, carpet underlays, etc., is polyurethane foam. Such foam is prepared by the reaction of a multifunctional polyester or polyether polyol with a polyfunctional isocyanate in the presence of water and often a blowing agent. This low density cellular material is both economical to manufacture as well as versatile in fabrication capability to allow formation of different shapes and sizes of foam.
Two key attributes of a comfort cushioning material are, first, a soft initial touch or feel followed by, second, a significant support or load bearing upon further penetration into the foam as the person's weight is applied thereto by sitting or lying thereon. This character of a foam is termed the Support Factor and is numerically defined as the ratio of load bearing capability at 65% deflection to the load bearing capability at 25% deflection. As determined by ASTMD-3574, the Support Factor is the ratio of 65% Indentation Force Deflection to 25% Indentation Force Deflection.
Prior to the present invention the available polyurethane foam materials, at a reasonable commercial density, had a Support Factor in the range of about 1.8-2.6. While this fairly narrow range sufficed for many cushioning needs, a large segment of the market requires a much larger Support Factor in such materials.
Prior to the present invention, larger Support Factor materials were attained by any of several time consuming and expensive procedures. In one such procedure two foams, each differing in degree of firmness or hardness, were adhesively laminated to form a composite which had a soft initial feel followed by deep support provided primarily by the firmer foam. In an extreme case, the softer foam of the laminate was a convoluted foam which yielded an extreme initial softness. Another common method of providing a cushion having a soft initial touch upon being seated followed by deep support has been to adhesively laminate a bonded, nonwoven, synthetic fiber composition to the surface of the cushioning material. This soft nonwoven foam composite provides a soft space filling along with a firm support, which support is dependent on the polyurethane foam which is utilized.
These methods of providing a broad range of support factor involve expensive multi-step operations and, very often, a plurality of materials, such as nonwoven fibers, adhesives, and the like.
Flexible, densified foams are also known in the art and their use as rug padding, cushions, mattresses, etc. has been suggested. U.S Pat. Nos. 3,506,600 and 3,709,843 disclose a process for preparing a flexible, densified polyurethane foam having a density between about 1.5 to about 15 pounds per cubic foot. A polyurethane foam-forming reaction mixture is allowed to rise in a reaction zone to form a partially cured cellular material and then a compressive force is applied thereto within a period of from 0 to 10 minutes after the completion of the rise. The compressive force reduces the volume of the partially cured cellular material to between about 2/3 to about 1/10 of the original volume. The compressive force is removed and the curing of the compressed cellular material is then completed. The time between the completion of the rise and the application of the compressive force depends upon the environmental temperature of the partially cured cellular material.
The densified foams made by the process of U.S. Pat. No. 3,506,600 are alleged to have a Support or Sac Factor of between about 2-3 to about 10 and such foams allegedly have little tendency to "bottom-out". The term "bottom-out" or "bottoming-out" is stated to be employed in the cushioning trade to describe a foam in which there is a sensation of sinking through and hitting the bottom when someone sits on it.
U.S. Pat. No. 3,658,972 describes a process for making a flexible molded densified polyurethane foam having at least two integral sections of different densities and useful in making a molded bucket seat for automobiles, which process incorporates to a large extent the process of U.S. Pat. No. 3,506,600. U.S. Pat. No. 3,787,278 discloses a flexible, molded, densified polyurethane foam prepared from a single foam formulation and having at least two integral sections of different densities. U.S. Pat. No. 3,867,320 discloses a densified polyurethane foam which is flame retardant. U.S. Pat. No. 3,650,993 discloses a process for preparing a flexible densified polyurethane foam whereby the thickness of undensified polyurethane foam layers integral with the densified foam is reduced, which process utilizes particular foaming agents. U.S. Pat. No. 3,709,966 discloses a process for making a polyurethane foam composite having a plurality of bonded layers wherein at least one of the layers is a flexible, densified polyurethane foam.
Apparatus suitable for making densified foam is known and is disclosed in U.S. Pat. Nos. 4,134,945, 4,252,517, 4,338,072 and 4,344,902.
While densified polyurethane foams, as described in the above patents, have been known in the art, and their use as seat cushions, mattresses, bucket seats, rug underlays, etc. have been suggested, foams prepared using the teachings of these patents, when made into seat cushions, were found to yield an uncomfortable character despite their moderately large Support Factor. This uncomfortable character has been described as a dead feel with a lack of springiness.